Downlink in current radio cellular communications generally refers to that a base station sends a signal to a terminal UE. In a Long Time Evolution (LTE) system of the 3rd Generation Partnership Project (3GPP), downlink physical channels may be divided into a data channel, a control channel, a broadcast channel, a synchronization channel, a paging channel, a multicast channel, and the like according to functions. A downlink physical data channel in LTE includes a physical downlink control channel (PDCCH, Physical Downlink Control Channel), a physical control format indicator channel (PCFICH, Physical Control Format Indicator Channel), and a physical HARQ indicator channel (PHICH, Physical Hybrid ARQ Indicator Channel). In addition, broadcast information is transmitted in two parts, where a most basic master information block (MIB, Master Information Block) of the broadcast information is transmitted on a physical broadcast channel (PBCH, Physical Broadcast Channel), and another remaining system information block (SIB, System Information Block) of the broadcast information is transmitted on a PDSCH.
Content transmitted on a PDCCH channel is downlink control information (DCI, Downlink Control Information), which corresponds to downlink and uplink control information. For example, after allocating and scheduling some resources to a UE, a base station (eNodeB) needs to indicate, to the UE, information such as a position, a size, and a modulation manner of these resources on a PDSCH, and for another example, uplink power control information and an uplink resource grant are both informed to a UE through the PDCCH. After a UE demodulates its own DCI, data can be further demodulated on a PDSCH according to the control information. Because a type of control information that is corresponding to a different transmission mode or situation and required by a UE is very different, different DCI formats are defined in LTE to classify the DCI, and merely control information that is corresponding to a current situation and required by the UE needs to be placed in the DCI, with no need to place control information under all situations in one piece of DCI for transmission, thereby reducing an overhead of downlink control information to a great extent. Because content of the DCI is 0-1 bit, the DCI cannot be directly sent, and a series of processing is further required. In LTE, something obtained after the DCI undergoes a series of processing procedures such as channel coding and modulation is called a CCE.
A PBCH is a physical broadcast channel defined in LTE, and is used for transmitting broadcast information, where content thereof is an MIB with 14-bit information. The PBCH does not appear in each subframe (each subframe lasts for 1 millisecond), but appears four times in one cycle, where every 40 milliseconds are one cycle. The MIB stores most basic broadcast information, which includes 4-bit bandwidth information, 2-bit PHICH configuration information, and an 8-bit system frame number. All remaining broadcast information SIBs are transmitted on a PDSCH.
A PHICH is used for transmitting an HARQ response of a physical uplink data channel, that is, an eNodeB informs, by using this channel, a UE whether a certain block of data on the physical uplink data channel of the UE is transmitted successfully. A PCFICH is used for indicating that in a current subframe, the first several OFDM symbols are used as control channels (PDCCH, PHICH, and PCFICH).
In a discussion of 3GPP LTE Release 11, the following scenario is involved: Several other base stations (remote radio unit (RRHs) or antenna unit (AUs)) are deployed in a coverage area of a base station, where in the 3GPP, these additional base stations (RRHs or AUs) and the original base station are collectively called a transmission point (TP), and the TP is more a name in a logical sense. In a typical scenario of the 3GPP, a cell ID same as that of an original base station is configured for all additionally deployed base stations in a coverage area of the original base station (which is generally a macro base station). Because in an existing system of LTE Release 10 or an earlier version, one cell ID uniquely corresponds to one TP, when the existing system of LTE Release 10 or an earlier version are used for a plurality of TPs having a same cell ID, a problem that cannot be solved in the prior art occurs, for example, a problem that a control channel capacity is limited. That a control channel capacity is limited refers to that in a scenario in which a plurality of TPs have a same cell ID, because each TP serves several UEs, the total number of UEs in a cell is several times that in a scenario in which one cell ID uniquely corresponds to one eNodeB. Therefore, a situation that a capacity of a control channel (for example, a PDCCH) is insufficient occurs. In addition, because a UE can demodulate a data channel only after demodulating its control information, if no control channel resource is allocated to the UE, data transmission of the UE cannot be performed. Therefore, system throughput is limited by the capacity of the control channel.